1. Field of the Invention
The present invention generally relates to a router and a method of changing a fragment size of data packets, and particularly relates to a router connected to a network conveying data packets and audio packets and a method of changing a fragment size of data packets that are supplied to the network.
2. Description of the Related Art
FIG. 1 is an illustrative drawing for explaining a VoIP (voice over internet protocol) router.
As shown in FIG. 1, a VoIP router 11 is provided between a WAN (wide are network), a LAN (local area network), and a PBX (private branch exchange) 10. The VoIP router 11 converts data signals and audio signals into packets when the data signals are supplied from the LAN, and the audio signals are supplied from the PBX 10, and sends the packets to the WAN. When receiving data packets and audio packets from the WAN, the VoIP router converts these packets into data signals and audio signals, which are then supplied to the LAN and the PBX 10, respectively.
The VoIP router 11 establishes interface with the LAN, the WAN and the PBX 10.
In the VoIP router 11, there is a need to avoid making an audio frame wait until transmission of a packet to the WAN is finished where the packet may be such a long packet as that of FTP (file transfer protocol) or HTTP (hypertext transport protocol). To this end, such a long packet is divided, and audio packets are inserted therebetween. This is called fragmentation. The VoIP router checks an MTU (maximum transfer unit) size of the IP (Internet protocol) layer. When the router receives a packet having a size exceeding the MTU size, the router notifies, via ICMP (Internet control message protocol), the source of the packet that the excess size of the packet creates errors, and notifies the source how large the MTU size is. An apparatus at the packet source adjusts the packet size to the MTU size, and transmits packets having a shorter size.
In this configuration, when the VoIP router receives a packet having a size exceeding the MTU size, the VoIP router arranges for the source to transmit shorter packets matching the MTU size. Alternatively, the VoIP router may change the packet to a shorter packet that conforms to the MTU size.
Data that is transmitted via FTP or HTTP forms a packet as large as 1000 bytes, for example. Audio packets, on the other hand, have a size that is as small as a two-digit figure in byte.
FIG. 2 is an illustrative drawing for explaining transmission of data from a router.
As shown in FIG. 2, a long packet D may be divided into shorter packets D1 through D5, which are then transmitted to the WAN while audio packets V1 through V4 having priority are inserted between the shorter packets D1 through D5. Even in this case, transmission of the audio packets may be delayed if the MTU size is relatively large, thereby degrading audio quality.
For example, if the MTU size is so large that the data packets D1 through D5 are significantly larger than the audio packets V1 through V5, the audio packets V1 through V3 are delayed by the data packet D5, and the audio packet V1 is further delayed by the data packet D4.
In general, the shorter the fragment size of data, the higher the audio quality is. However, improvement in the audio quality is achieved at the expense of the throughput of data communication. Accordingly, if sufficient audio quality is being maintained, the fragment size of data may be lengthened to boost the throughput of data communication.
Conventionally, the MTU size is fixed, and does not change dynamically to cope with situational changes.
Accordingly, there is a need for a scheme that can automatically change a fragment size of a data packet so as to keep audio quality within a predetermined range.